New Theories of Depression Focus on Brain's Two Sides

By SANDRA BLAKESLEE

Published: January 19, 1999

Two new theories of depression are rekindling interest in the once fashionable topic of how the left and right sides of the human brain interact.

At a meeting of the Society for Neuroscience last November in Los Angeles, Dr. Jack Pettigrew, a neuroscientist at the University of Queensland in Brisbane, Australia, proposed that people with manic depression have a ''sticky switch'' somewhere deep in their brains.

In normal people, the switch allows either the left or right hemisphere to be dominant during different mental tasks, with the two sides constantly taking turns. In people with manic depression, one hemisphere becomes locked into a dominant position in periods of depression while the other hemisphere is locked at times of mania. In a truly bizarre finding, Dr. Pettigrew reported that the placement of ice water into one ear seems to unstick the switch.

The second theory is being put forth by Dr. Frederic Schiffer, a psychiatrist at Harvard Medical School. He maintains that one hemisphere can be more immature than the other and that this imbalance leads to different mental disorders. Dr. Schiffer has designed special goggles to help people ''talk'' to each half of the brain separately, to learn which is less mature, and to bring the two hemispheres into harmony.

Both ideas have been well received by brain lateralization authorities eager to see a revival of their specialty.

''It's nice to see the left and right hemispheres are back,'' said Dr. Brenda Milner, a cognitive neuroscientist at the Montreal Neurological Institute in Quebec. The notion that the human brain has two halves and that the left side is associated with logical, analytical thinking while the right side is more intuitive, emotional and creative was popularized about 20 years ago, she said, and soon became received wisdom about how the brain works. ''This idea fell from fashion not because people didn't like it but because they got interested in other things,'' she said.

Dr. Marcel Kinsbourne, a cognitive scientist at the New School for Social Research in New York City and early pioneer in brain lateralization studies, believes that left and right brain ideas also fell from fashion because they were oversold. People looked for universal dichotomies -- the left brain is a whiz at legal briefs but the right brain is deft at poetry -- that carried things too far. But the new theories are ''intriguing,'' Dr. Kinsbourne said, although they have a long way to go before they can be accepted as valid. ''We are in half-baked land here,'' he said.

The new theories are also appealing to many experts because they take on a question that has divided researchers for decades. Do people have one overarching mind that spans the two hemispheres? Or are they born with two separate minds -- one on the left and one on the right -- which operate so seamlessly that the person simply does not notice that there are two?

The subjective sense of having just one mind is overwhelming and unmistakable, said Dr. Joseph Bogen, a neurosurgeon at the University of Southern California in Los Angeles. But if the thick band of fibers connecting the two hemispheres is severed, he explained, humans seem to end up with two separate minds that show different abilities. In one dramatic disparity, the left hemisphere does all the talking while the mute right hemisphere has better access to emotions. For example, when the right brain is shown a photograph, the talkative left brain will say that it does not see anything and cannot comment. But the left hand, which is connected to the right brain, can raise a thumb up or down in response to the question, ''Do you like the picture?''

These kinds of experiments led to a dichotomy of opinion among neuroscientists, Dr. Bogen said. One camp held that in splitting the brain, a single mind is cut into two but that it is abnormal to have two brains. The other camp said every person is born with two brains but because the two sides get along so well, people simply have the illusion of one mind.

After thousands of experiments carried out on normal subjects and split-brain patients, scientists still passionately disagree. But one feature has clearly emerged, said Dr. Terry Sejnowski, a neuroscientist at the Salk Institute in San Diego: Human brains show enormous variation in lateralization.

The claim that certain talents or abilities lie in one hemisphere or the other is usually based on averaging the brains of many people, he said. Because each individual brain is a complex system that evolves in response to a unique environment, many brain functions do not end up in the same place. This is further complicated by the fact that the left and right hemisphere probably communicate through deeper pathways that are not affected in split-brain patients.

The new ideas about lateralization will not resolve the question of one versus two brains, but they do add insights and suggest new ways to treat mental patients, said Dr. Schiffer, whose research was set off by his observation that many of his patients seemed to have a kind of double personality.